1. Field of the Invention
The present invention relates to conveying workpieces in a workpiece decorating machine and, more particularly, to imparting traveling motion to workpieces for delivery to and from a decorating station at which traveling motion is interrupted by a dwell period to allow the application of decoration to the workpiece.
2. Description of the Prior Art
As shown in U.S. Pat. Nos. 2,231,535; 2,261,255; 2,721,516; 3,146,705; and 5,524,535 intermittent motion type decorating machines are known in the art and provide an indexing drive system to impart intermittent traveling motion to an endless conveyor chain used to supply workpieces such as containers made of glass or plastic. A container is moved by the endless chain conveyor through a predetermined distance, stopped, moved again through a predetermined distance, stopped and again moved until each container through the sequence of motions moves completely through each of a predetermined number of decorating stations of the decorating machine. A decorating station will be provided at one or more places where the container comes to a stop. At each decorating station while the container is stopped from traveling motion, a decorating screen is displaced into line contact by an associated squeegee with the surface of the container while the container is rotated about a longitudinal axis thereof. During the decorating process a synchronous speed relation is maintained between the linear speed of the screen undergoing linear displacement and the speed of rotation of the container at the line of contact established by the squeegee. The squeegee remains stationary during the decorating process. Decorating machines of this type are particularly useful to decorate bottles and carryout the decoration while the surface of the bottle being decorated is horizontally orientated. In the aforesaid U.S. Pat. No. 2,261,255 there is disclosed a drive for moving each of a screen to decorate a cylindrical body of a bottle and a shoulder screen to decorate a tapered neck portion of the bottle substantially at the same peripheral linear speed. The decorating machine disclosed in the aforesaid U.S. Pat. No. 3,251,298, provided a production rate of about 125 bottles per minute. More recently as disclosed in U.S. Pat. No. 5,524,535 a decorating machine design is provided to increase the production rate of up to 150 bottles per minute. In this decorating machine, the machine cycle is altered to attain the increased production rate. The altered machine cycle provides that the portion of the cycle for conveyor indexing has a reduced duration in order to provide an increased part of the machine cycle for decorating. The reduced cycle for indexing places increased demands for indexing power requirements and number of chains and sprockets to reduce unwanted chain stress. At such production rates, the start and stop events of the intermittent advancement of the endless conveyor impose severe stress and strain on the entire conveyor system including the drive therefore. Typically such a conveyor includes spaced apart horizontal shafts one of which is driven by an indexer drive and the other is an idler shaft. Each shaft supports at least two and sometimes three or more spaced apart sprockets. Wear of the sprocket teeth can be reduced by increasing the number of sprockets and associated chains thereby reducing the loading on each sprocket; however, by increasing the number of sprockets and chains, the power requirements for the indexer drive increase since the mass represented by the conveyor that must be indexed is increased. A sprocket on the driven shaft and the sprocket on the idler shaft engage with an endless chain made up of links connected with carriers for workpieces. The idler sprocket is rotatably supported by bearings and acted upon by a spring loaded tensioner to impose a predetermined tension on the endless chains engaged with the respective sprockets.
In such intermittent motion decorating machines, thermosetting ink was usually the printing medium particularly when multiple color decoration was desired. Ink of only one color is applied at each decorating station and to decorate with multiple colors requires a corresponding multiple decoration stations. When the different-colors interleave in a given area of the bottle, the same area is contacted with the screens for each color and therefore it is necessary that the applied ink/color is a solid and will not smear when additional ink/color is applied. Although the ink is solidified after each printing operation, it was necessary to cure the ink by feeding the bottles through a furnace after discharging from the decorating machine. In co-pending patent application Ser. No. 09/079,753 filed May 15, 1998 there is disclosed a decorating method and apparatus to allow curing of ink decoration applied at one station before additional decoration is applied so that the decoration on a bottle delivered from the decoration machine is cured and the bottle can be loaded directly into a shipping container without the need for curing the ink decoration. The decorating medium is chosen to cure very rapidly when exposed to a source of electromagnetic waves such as ultraviolet radiation or heat. Curing stations are interleaved between printing stations and provided with drives to rotate the bottle at the curing station for exposing uncured printing medium to the electromagnetic wave or heat to curing the printing medium. The dwell period of the intermittent advancing motion by the conveyor chain is used to apply decoration and to cure the applied decoration all at difference spaced apart sites along the course of travel by the bottles in the decorating machine.
The present invention seeks to provide a traveling motion for workpieces interrupted only at a work station which can be the printing station and when desired a curing station in an intermittent motion type decorating machine in a manner representing a complete departure from the conventional practice of using a chain conveyor to support workpieces while intermittently advanced by operation of an indexer drive. The conveyance of workpieces particularly bottles, for example, in intermittent type decorating machines provides that each bottle must dwell at a decorating station for a period of time sufficient to apply the desired decoration. At the decorating station, silk screen printing technique is used for the application of the decoration to a workpiece. This printing technique requires a precise relationship formed by moving the squeegee to establish line contact between a linear moving screen and the rotating surface of the bottle. The line contact established by the squeegee must be in a horizontal plane which is a tangent to the decorating site. The repetitious starting and stopping of the conveyor causes elongation of the metal links due to wear in response to the stress and strain of the conveyor operation. Conveyor stretch adversely affects the relationship between a bottle at a decorating station and the operating position of the squeegee as well as registration of the silk screen relative to the bottle at the decorating station. The conveyor stretch also degrades the accuracy of seam alignment at the indexing operation used to orientate a bottle immediately after loading onto the conveyor chain. A lack of registration of the decoration and the likelihood of smearing of the printing will occur in the event the intermittent motion of the chain conveyor brings a bottle to rest slightly before or slightly after the preselected site for the decorating operation. Also, a misalignment between the longitudinal axis about which the bottle is rotated and a rotational axis about the bottle rotator drive causes a mismatch to the required synchronous speed relation between decorating screen and bottle.
Stretch of the conveyor chain can be compensated by adjustments to the position of the squeegee and screen along the course of travel by the conveyor chain. Eventually the connections between chain links where resulting in excessive clearance with also contributes to an elongation of the conveyor chain. The arrangement of parallel conveyor chains must transmit the torque necessary to achieve the rapid intermittent motion to control movement of not only the mass of the chains and idler sprocket but also the bottle carriers and bottles supported by the carriers. Required operating clearances and the manufacturing tolerance between pivotal surfaces of parts forming chain links typically produce a variation to the chain pitch of 1/1000 of an inch between chain links. If there are, for example, 62 chain links forming each endless chain, the manufacturing tolerance presents a total of 62/1000 of chain links variation which adversely effects the need for an exact positioning of each bottle carrier at a decorating station. The condition clearly becomes worse as the number of links in each continuous chain increases. The mass of the conveyor increases when the size of the link increase which imposes an adverse effect to the drive requirements for the indexing drive. These tolerances presents unwanted variations to the separating distance between carriers. The rapid starting and stopping of the carrier laden chains generate noise, the level of which increases with the indexing rate per minute. Stretch of the chain links occur continuously with the operation of the conveyor and when the quality of registration degrades or at scheduled maintenance intervals, compensating adjustments must be carried out usually at intervals of several months. It has been found that typically chain link stretch and wear between pivotal parts of the chain links degrade the operation of the conveyor beyond acceptable limits and requiring replacement of the chains on an annual basis given normal hours of operation of the decorator.
Workpiece registration at the printing stations is established by adjusting each printing station relative to the location of a workpiece during a dwell period. Not only must the printing stations be adjusted relative to the decorating position of the workpiece but also the indexing registration station and the bottle loading equipment requires similar position correcting adjustments. Chain stretch and the dimensional tolerances between links are factors which limited the length of a conveyor that can be provided in a decorating machine. At each decorating station there is a rotator drive head provided with a slotted opening to receive a roller on the end of a crank arm by which a bottle is rotated for the decorating process. The rotational axis of the bottle and the rotational axis of the drive head must be aligned to produce a uniform rotational speed of the bottle surface to which decoration is applied. Chain stretch causes a misalignment resulting in a nonconcentric rotation between the rotational axis of the bottle and the rotator. As a result, the applied decoration is distorted because of slippage due to the mismatch of speeds between the screens and the bottle surface.
The present invention eliminates the requirement to rapidly accelerate and decelerate a carrier laden chain conveyor containing all bottles or workpieces processed in a decorating machine by providing that only those workpiece laden carriers discharged from a decorating station and entering an empty decorating station are accelerated to a continuous advancing movement. All remaining carriers are advanced by a continuous motion which according to the preferred embodiment, the continuous motion is at a constant speed. The torque requirement to convey workpieces is greatly reduced by this arrangement and the speed at which workpiece laden carriers are advanced from decorating station and to decorating station as well as executing return travel from the exit to the entry end of the decorating machine can be increased significantly to speeds that are not believed obtainable in a conventional chain conveyor system.
It is an object of the present invention to provide a workpiece conveying system wherein only a workpiece discharged from the decorating station and a workpiece entering a decorating station are accelerated from a rate of travel at a continuous speed and wherein workpiece carriers are returned from a discharge end of a decorating machine to the entry end of a decorating machine at a rate of travel which is of a continuous speed.
It is an object of the present invention to provide a workpiece conveying system wherein only a workpiece discharged from a dwell station and a workpiece entering an empty dwell station are accelerated from a rate of travel at a continuous speed, the dwell station being plural in number and include a decorating station and a curing station for printing medium applied at a decorating station and wherein workpiece carriers are returned from a discharge end of a decorating machine to the entry end of a decorating machine at a rate of travel which is of a continuous speed.
It is an object of the present invention to provide a workpiece conveying system supplying a dwell period wherein workpieces are not subject to conveying motion while decorated at decorating stations and at all other times the workpieces are advanced by a continuous motion.
It is another object of the present invention to continuously convey workpieces to and from decorating stations on carriers that are independent and discrete from one another.
It is another object of the present invention to provide a workpiece conveying system having cam tracks in barrel cams to impart traveling motion to carriers with and without workpiece in an endless fashion for an intermittent motion type decorating machine.
It is another object of the present invention to provide a tandem arrangement of barrel cams driven to rotate about a common longitudinal axis for advancing a plurality of separate and independent workpiece carriers along continuous cam tracks of the barrel cams and a carrier transfer disk between the tandem arrangement of cams for delivering a workpiece carrier from a cam track in one of the tandemly arranged barrel cams to the cam track of the other tandemly arranged barrel cams and thereby provide a conveyor system for an intermittent type decorating machine of an unusually great length and an unusually low torque requirement for a multiplicity of decoration operations without the need to provide more than one decorating machine.